Don't worry, Lil, I get those two spellings confused all the time.
Since we started the conversation, I decided to do a bit of research because you don't dangle a question like that in front of a philologist and not get her to do research on it:
So the -nn- word (
cannon) referring to the weapon seems to go back via French to a Romance language word meaning "tube" or "barrel". This in turn is possibly related to the word from which we get
cane (as in "a stick") which originally meant something like "reed" (so
cane = small hollow stick/tube;
cannon = big hollow stick/tube).
Cane does seem to go all the way back to Latin
canna which comes from Greek
kanna (which might ultimately derive from a Semitic word).
Here's the etymological entry in the OED:
cannon
Forms: Also 15thC (chanon), 15–17thC canon.
Etymology: In 16th cent. also canon , Scottish cannoun , < French canon (14th cent. in Littré) = Provençal canon, Catalan canó, Spanish cañon , Italian cannone , lit. ‘great tube, barrel’, augmentative of canna, canne = cane n.1, reed, pipe, tube. The spellings canon and cannon occur side by side down nearly to 1800, though the latter is the more frequent after c1660
Notice that until 1800, single and double -n- spellings were used
Now the single -n- word (
canon) referring to an established text has a complicated origin. It seems to have been originally applied to rules or laws introduced by the Church (and is still used in that sense today - "a canon of the church"). Among these laws was the "canon of scripture" (officially established books of the bible). Later it was also used of other "canonical" lists of works by secular authors like "The canon of Shakespeare" or "The canon of Greek orators". We now use it basically as an adjective to describe an adaptation (like a film) that sticks to the original text of the author or to refer to something that exists in the imaginary world/universe established by the creator of that world/universe (like the "canon of Star War"s which they rudely decided to mess with recently
)
The actual etymology of
canon is apparently from Latin
canon and Greek
kanon which according to the etymology means "rule". But when I looked those words up (
kanon isn't the normal Greek word for "rule") it actually refers to a straight rod or bar which can be used as a unit of measure (like a modern-day ruler). Which means (guess what?)....it turns out this word is related to the
kanna word meaning "reed" -
So it looks like both words have a similar origin after all !!
Etymology from OED
canon
Forms: ME canoun, (ME canown), 15–17thC cannon, OE, ME– canon.
Etymology: Found in Old English as canon , < Latin canon rule, < Greek κανών rule. Early Middle English had ˈcanon , probably < Old English, and caˈnun , caˈnoun , < Old French canun , canon , the French descendant of the Latin. Senses 12 – 14 are of obscure origin; some or all may belong to cannon n.1 in French spelt canon
(etymologies taken from OED.com which is the official home of the Oxford English Dictionary online - a website not affiliated with TLC)